A PT ferromagnetic resonance self-adaptive cooperative suppression method and system

Abstract

The application discloses a PT ferromagnetic resonance self-adaptive cooperative suppression method and system, comprising the following steps: monitoring voltage signals, current signals and PT secondary side voltage signals of a real-time sampling high-voltage end sensing unit, calculating a primary side voltage change rate and harmonic content; comparing the calculated primary side voltage change rate and harmonic content with corresponding preset threshold values, controlling the input of a neutral point reconstruction unit, and destroying the resonance condition by changing the neutral point grounding impedance; after the neutral point reconstruction unit works, controlling the input of an energy feedback unit for absorbing resonance energy; when detecting that the resonance threat is eliminated, controlling the neutral point reconstruction unit and the energy feedback unit to be turned off in sequence, and starting active cooling of the high-voltage end sensing unit by using the remaining energy in the energy feedback unit. The method can realize system safety recovery by monitoring the voltage change rate and harmonic content in real time, quickly triggering the neutral point reconstruction to destroy the resonance, and absorbing and feeding back the energy by using the energy feedback unit.

Description

Technical Field

[0001] This invention relates to the field of power system overvoltage protection technology, and more specifically, to a PT ferroresonant adaptive cooperative suppression method and system. Background Technology

[0002] Ferromagnetic resonance in PT (electromagnetic voltage transformer) systems is one of the most common and dangerous overvoltage faults in ungrounded neutral systems. When the system is subjected to disturbances such as switching overvoltages or recovery from single-phase ground faults, the magnetic flux of the PT core will rapidly saturate, causing a nonlinear jump in its magnetizing inductance. This leads to a resonant circuit with the system's capacitance to ground, resulting in neutral point voltage shift and a sharp amplification of harmonic components. This can cause serious accidents such as PT fuse blowout or even equipment insulation breakdown.

[0003] Currently, traditional ferromagnetic resonance suppression measures mainly include the following:

[0004] Fixed grounding resistance method: A damping resistor with a fixed value is connected in series at the neutral point of the PT. Although this method is simple and reliable, its damping characteristics are fixed and cannot adapt to changes in system operation (such as changes in ground capacitance caused by line switching). If the resistance value is too small, the damping effect will be insufficient; if it is too large, it will affect the accuracy of normal zero-sequence voltage measurement and may cause the PT to bear overcurrent risk in the event of a single-phase ground fault.

[0005] Primary harmonic suppressors typically employ nonlinear resistive materials. While their current-voltage characteristics offer some self-adaptation, they are fundamentally passive energy-dissipating components, relying on converting resonant energy into heat for energy dissipation. This not only leads to energy waste but may also affect equipment lifespan due to prolonged heating and carries the risk of thermal breakdown under continuous resonance.

[0006] Secondary microcomputer-based harmonic suppression device: This device triggers the switching of resistors by monitoring the open delta voltage of the PT. The main bottleneck of this scheme is the response lag. It can only operate after the PT core is deeply saturated and the secondary voltage distortion is fully manifested. This makes it difficult to achieve rapid suppression during the "golden window" of resonance and easily misses the best control opportunity.

[0007] In summary, existing technologies generally suffer from inherent contradictions among "response speed and suppression depth," "adaptive capability and system impact," and "energy handling methods." Specifically, these contradictions manifest as: either slow response, preventing proactive intervention; poor adaptability, failing to dynamically track changes in system parameters; or crude dissipation of resonant energy, leading to additional thermal stability and economic problems. Therefore, power systems urgently require an intelligent, adaptive, and collaborative suppression scheme that integrates rapid early warning, proactive reconfiguration, and energy recycling. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a PT ferromagnetic resonance adaptive cooperative suppression method and system, which achieves rapid suppression of ferromagnetic resonance and safe system recovery through the cooperative control of early warning reconstruction, energy management and adaptive recovery.

[0009] To achieve the above objectives, in a first aspect, the present invention provides a PT ferromagnetic resonance adaptive cooperative suppression method, comprising:

[0010] The voltage signal, current signal and PT secondary voltage signal monitored by the high-voltage end sensing unit are sampled in real time, and the primary side voltage change rate and harmonic content are calculated.

[0011] Based on the calculation of the primary voltage change rate and harmonic content, and the comparison with the corresponding preset threshold, the neutral point reconstruction unit is controlled to be put into operation, and the resonance condition is destroyed by changing the neutral point grounding impedance.

[0012] After the neutral point reconstruction unit is operational, the energy feedback unit is controlled to absorb resonant energy and feed it back to the power system.

[0013] Once the resonance threat is detected and eliminated, the control sequentially shuts down the neutral point reconstruction unit and the energy feedback unit, and uses the remaining energy in the energy feedback unit to initiate active cooling of the high-voltage sensing unit.

[0014] Preferably, the high-voltage sensing unit is connected between the high-voltage terminal of the PT primary side and the system bus, and is used to collect the PT primary side voltage and current signals in real time, including a PTC thermistor and a current transformer connected in series.

[0015] The neutral point reconfiguration unit is connected between the PT neutral point and ground, and is composed of a first switch and an adjustable inductor connected in series.

[0016] The energy feedback unit is connected in parallel with the neutral point reconfiguration unit and is composed of a second switch, a bidirectional DC / AC converter, and a DC-side support capacitor connected in series.

[0017] Preferably, the neutral point reconstruction unit is controlled based on the calculated primary side voltage change rate and harmonic content, and the resonance condition is disrupted by changing the neutral point grounding impedance. The specific process is as follows:

[0018] The primary voltage change rate is set as the main criterion. When the primary voltage change rate exceeds the preset first threshold, the first switch is immediately triggered to close, and the neutral point reconstruction unit is put into operation.

[0019] After the complete harmonic analysis is finished and the harmonic content is obtained, the harmonic content is compared with the preset second threshold:

[0020] If the harmonic content is less than or equal to the preset second threshold, it is determined that no resonance characteristic has occurred, and the first switch is turned off, and the neutral point reconstruction unit is launched.

[0021] If the harmonic content is greater than the preset second threshold, it is confirmed that ferromagnetic resonance has occurred, and the neutral point reconstruction unit is maintained.

[0022] Preferably, the process for determining the value of the adjustable inductor is as follows:

[0023] While the neutral point reconfiguration unit is being put into operation, the system ground capacitance and PT excitation inductance are estimated based on the current signal monitored by the current transformer and the secondary voltage signal of the PT, and the main frequency of the current resonance is determined.

[0024] The type of resonant frequency is determined based on the main frequency, the target value is calculated using the corresponding formula, and the adjustable inductor is adjusted to the target value.

[0025] Continue monitoring. If the resonance is not suppressed, adjust the adjustable inductor in a preset step size near the target value until the resonance is suppressed, and record the corresponding frequency and inductance value.

[0026] If resonance is suppressed, keep the adjustable inductance at the target value and record the corresponding frequency and inductance value.

[0027] Preferably, after the neutral point reconstruction unit operates, the energy feedback unit is controlled to absorb resonant energy and feed it back to the power system. The specific process is as follows:

[0028] After the neutral point reconstruction unit operates, if the harmonic content is detected to be greater than the preset second threshold within the preset time threshold, the second switch is closed and the energy feedback unit is started.

[0029] If the harmonic content is not detected within the preset first time threshold, the second switch will be closed directly when the preset first time threshold is reached, and the energy feedback unit will be started.

[0030] By using PWM modulation of a bidirectional DC / AC converter, resonant energy is absorbed into the DC-side support capacitor and inverted into power frequency energy to be fed back to the system or load, thus achieving smooth energy absorption and feedback.

[0031] Preferably, after the resonance threat is detected and eliminated, the neutral point reconstruction unit and the energy feedback unit are sequentially shut down, and the remaining energy in the energy feedback unit is used to initiate active cooling of the high-voltage sensing unit. The specific process is as follows:

[0032] When the detected harmonic content is lower than the preset third threshold and the duration reaches the preset second time threshold, the first switch and the second switch are turned off in sequence.

[0033] The system compares the temperature of the PTC thermistor, which is detected in real time, with a preset temperature threshold. If the temperature of the PTC thermistor is higher than the preset temperature threshold, the remaining energy in the energy feedback unit is used to start active cooling of the PTC thermistor until it reaches below the standard value.

[0034] Secondly, the present invention provides a PT ferromagnetic resonance adaptive cooperative suppression system, applied to the above-mentioned PT ferromagnetic resonance adaptive cooperative suppression method, comprising the following modules:

[0035] The collaborative suppression module is used to monitor signals in the circuit system, provide early warning of resonance, and instantaneously change the neutral point impedance parameter of the system after the resonance begins to disrupt the resonance condition, and absorb and feed back the resonance energy in the system.

[0036] The central control module is used to receive signals monitored by the cooperative suppression module and control the operation of the cooperative suppression module.

[0037] Preferably, the cooperative suppression module includes a high-voltage end sensing unit, a neutral point reconstruction unit, and an energy feedback unit; wherein,

[0038] The high-voltage sensing unit is connected between the high-voltage terminal of the PT primary side and the system bus, and is used to collect the voltage and current signals of the PT primary side in real time, including a PTC thermistor and a current transformer connected in series.

[0039] The neutral point reconfiguration unit is connected between the PT neutral point and ground, and is composed of a first switch and an adjustable inductor connected in series.

[0040] The energy feedback unit is connected in parallel with the neutral point reconfiguration unit and is composed of a second switch, a bidirectional DC / AC converter, and a DC-side support capacitor connected in series.

[0041] Preferably, it also includes a cooling module driven by the DC output of the energy feedback unit, used to rapidly dissipate heat from the PTC thermistor after the resonance threat is detected and eliminated.

[0042] Thirdly, the present invention provides a computing device for an adaptive cooperative suppression method for PT ferromagnetic resonance, comprising:

[0043] One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for performing the method.

[0044] The beneficial effects of this invention are as follows:

[0045] This invention enables early warning and rapid suppression of resonance by real-time monitoring of voltage change rate and high-frequency harmonics; it recovers and utilizes resonant energy through an energy feedback unit, reducing system losses and improving economic efficiency; and it coordinates neutral point reconstruction with energy feedback to avoid overvoltage and equipment damage. Attached Figure Description

[0046] Figure 1 This is a flowchart of the adaptive cooperative suppression method for PT ferromagnetic resonance of the present invention;

[0047] Figure 2 This is a block diagram of the PT ferromagnetic resonance adaptive cooperative suppression system of the present invention. Detailed Implementation

[0048] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0049] The terms "first," "second," and "third," etc., used in this specification and description of the drawings are used to distinguish different objects, rather than to limit a specific order.

[0050] In embodiments of the present invention, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" or "for example" in embodiments of the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0051] To ensure clarity and conciseness in the description of the following embodiments, a brief introduction to the related technologies is given first:

[0052] In ungrounded neutral systems, the most threatening overvoltage phenomena to the power grid are mainly of three types: lightning overvoltage, arcing grounding overvoltage, and ferroresonant overvoltage. Currently, relatively effective measures have been developed to prevent and control the first two types of overvoltages, but there are no very effective suppression measures for ferroresonant overvoltages. The research direction of ferroresonant overvoltages has received serious attention from experts and scholars both domestically and internationally. Significant progress has been made in its theoretical derivation, experimentation, and simulation, and harmonic suppression measures have also been developed to some extent. Some corresponding devices have been developed based on related principles. However, ferroresonant overvoltages still frequently cause accidents during actual system operation.

[0053] The mechanism of three-phase ferroresonance: In ungrounded neutral systems, electromagnetic voltage transformers with Y0 connections are used. Under normal operating conditions, the three phases of the PT are basically balanced, and the neutral point voltage of the power supply has almost no displacement. However, when disturbances occur in the system, such as closing an empty busbar or clearing a single-phase arcing ground fault, the neutral point potential of the power supply shifts relative to the ground potential, resulting in an unbalanced increase in the voltage of one, two, or even all three phases.

[0054] PTC resistors have very low resistivity at room temperature, which meets the requirements for normal operation of power systems. When the current increases and the resistor temperature rises, the resistivity of the PTC resistor increases rapidly, which can limit overcurrent and suppress overvoltage. Research on overvoltage suppression measures for voltage transformers based on PTC current-sensitive resistors is limited, and PTC current-sensitive resistors are mainly used for grounding the neutral point of the primary side of the PT. However, existing PTC materials can meet the requirements of high-voltage operation, and their ability to withstand large current surges has been greatly improved, enabling their application at the primary high-voltage end of the PT. PTC current-sensitive resistors can be applied to overvoltage suppression technology with series damping at the primary high-voltage end of voltage transformers.

[0055] In view of this, embodiments of the present invention provide an adaptive cooperative suppression method for PT ferromagnetic resonances, which can be executed by a processing device. This processing device can be a terminal or a server. Terminals include, but are not limited to, smartphones, tablets, laptops, personal digital assistants, or smart wearable devices. Servers can be cloud servers, such as central servers in a central cloud computing cluster or edge servers in an edge cloud computing cluster. Alternatively, servers can be located in a local data center. A local data center refers to a data center directly controlled by the user.

[0056] To address the shortcomings of traditional PT ferroresonant overvoltage suppression, such as slow response, poor adaptability, and susceptibility to secondary problems, this invention achieves rapid suppression of ferroresonant resonance and safe system recovery through coordinated control of early warning reconstruction, energy management, and adaptive recovery.

[0057] To make the technical solution of the present invention clearer and easier to understand, the following description, in conjunction with the accompanying drawings, introduces a PT ferromagnetic resonance adaptive cooperative suppression method provided by an embodiment of the present invention. Figure 1 As shown, this figure is a flowchart of an adaptive cooperative suppression method for PT ferromagnetic resonance provided by an embodiment of the present invention. The method includes:

[0058] S100: Real-time sampling of voltage signal, current signal and PT secondary side voltage signal monitored by the high-voltage end sensing unit; calculation of primary side voltage change rate and harmonic content.

[0059] The high-voltage sensing unit is connected between the primary high-voltage end of the PT and the system bus. It is used to collect the primary voltage (i.e., the voltage across the PTC thermistor) and current signal of the PT in real time. This includes the PTC thermistor and current transformer connected in series. Since the resistance of the PTC thermistor changes with its own power consumption (proportional to I²) and temperature, when the primary current changes drastically due to the onset of resonance, the voltage drop across the PTC thermistor will also change rapidly. Monitoring the secondary voltage signal of the PT is a well-known technique to those skilled in the art and will not be described in detail here. The secondary voltage of the PT is used to understand the fundamental operating state of the system.

[0060] Since the core of the PT may be saturated at the start of resonance, the distortion of its secondary output voltage will lag far behind the actual change on the primary side, making it impossible to reliably detect the rapid change at the start. The voltage signal across the PTC thermistor does not pass through the PT core and can more realistically reflect the dynamic process on the primary side. Therefore, the voltage change rate is calculated using the voltage signal across the PTC thermistor instead of the PT secondary side.

[0061] Perform a Fast Fourier Transform (FFT) on the current signal sampled from the current transformer. Extract the amplitude of each harmonic (e.g., 3rd harmonic at 150 Hz, 5th harmonic at 250 Hz, etc.) and the total energy of the high-frequency band (e.g., >1 kHz) from the FFT results, and calculate the total harmonic distortion rate or the content of a specific harmonic.

[0062] A software phase-locked loop is used to precisely lock the phase of the system's power frequency for a certain phase voltage on the secondary side of the PT. The amplitude of the power frequency fundamental wave is extracted from the PT secondary side signal through DFT or a filter.

[0063] Since the primary current is roughly proportional to the voltage (in non-saturation conditions), the fundamental current reference value on the primary side can be estimated using the fundamental voltage provided by the secondary side of the PT and the approximate impedance of the system. Alternatively, historical data from normal operation can be used directly as the fundamental reference.

[0064] The harmonic current measured by the current transformer is compared with this estimated fundamental current reference value to obtain the final harmonic content.

[0065] S200. Based on the calculated primary voltage change rate and harmonic content, compare them with the corresponding preset threshold, control the input of the neutral point reconstruction unit, and disrupt the resonance condition by changing the neutral point grounding impedance.

[0066] The primary voltage change rate is set as the main criterion. When the primary voltage change rate exceeds the preset first threshold, the first switch is immediately triggered to close, and the neutral point reconstruction unit is put into operation. Once this criterion is met, the neutral point reconstruction unit (closing the first switch) is immediately triggered without waiting for the complete harmonic analysis results, which aims to suppress the occurrence of resonance.

[0067] Simultaneously or shortly thereafter, the central control module performs FFT analysis on the signals of the current transformer and the secondary side of the PT. If the harmonic content exceeds the preset second threshold, it confirms that it is a ferroresonance and starts or maintains the energy feedback unit (closes the second switch). If the harmonic analysis results show no resonance characteristics (it may be a spurious disturbance), the neutral point reconstruction unit can be reset after a very short delay.

[0068] The process for determining the value of the adjustable inductor is as follows:

[0069] While the neutral point reconfiguration unit is being put into operation, the system ground capacitance and PT excitation inductance are estimated based on the current signal monitored by the current transformer and the secondary voltage signal of the PT, and the main frequency of the current resonance is determined.

[0070] The type of resonant frequency is determined based on the main frequency, the target value is calculated using the corresponding formula, and the adjustable inductor is adjusted to the target value.

[0071] Continue monitoring. If the resonance is not suppressed, adjust the adjustable inductor in a preset step size (e.g., ±10%, adjusted according to historical experience) near the target value until the resonance is suppressed, and record the corresponding frequency and inductance value.

[0072] If resonance is suppressed, keep the adjustable inductance at the target value and record the corresponding frequency and inductance value;

[0073] Establish a mapping database between system characteristic parameters and optimal inductance values ​​to accelerate the subsequent resonance suppression process.

[0074] Estimate the system's capacitance to ground and the PT magnetizing inductance, specifically:

[0075] The system's capacitance to ground can be estimated by collecting the current signal and the secondary voltage signal of the PT; the PT's magnetizing inductance can be estimated based on the PT's rated voltage and rated capacity.

[0076] The target value is calculated using the corresponding formulas, including formulas for frequency division resonance and high-frequency resonance, as follows:

[0077] For frequency division resonance, the formula is: target value = 1 / [(2πf)×C0]-Lm / 3, where f is the main frequency of the current resonance, C0 is the system capacitance to ground, and Lm is the PT excitation inductance; by connecting an appropriate inductor, the system resonance point is moved to a safe frequency range;

[0078] For high-frequency resonance, the formula is: target value = 1 / [(2π×150)×C0]-Lm / 3, where C0 is the system capacitance to ground and Lm is the PT excitation inductance; adjust the system parameters to be far away from the most likely third resonance point.

[0079] S300: After the neutral point reconstruction unit is working, the control input energy feedback unit is used to absorb resonant energy and feed it back to the power system.

[0080] After the neutral point reconstruction unit operates, if the harmonic content is detected to be greater than the preset second threshold within the preset time threshold, the second switch is closed and the energy feedback unit is started.

[0081] If the harmonic content is not detected within the preset first time threshold, the second switch will be closed directly when the preset first time threshold is reached, and the energy feedback unit will be started.

[0082] By using PWM modulation of a bidirectional DC / AC converter, resonant energy is absorbed into the DC-side support capacitor and inverted into power frequency energy to be fed back to the system or load, thus achieving smooth energy absorption and feedback.

[0083] S400: After the resonance threat is detected and eliminated, the control sequentially shuts down the neutral point reconstruction unit and the energy feedback unit, and uses the remaining energy in the energy feedback unit to start active cooling of the high-voltage end sensing unit.

[0084] When the detected harmonic content (i.e., total harmonic distortion rate THD, the ratio of the total effective value of all harmonic components to the effective value of the fundamental wave, obtained by analyzing the primary current signal monitored by the current transformer) is lower than the preset third threshold and the duration reaches the preset second time threshold, the first switch and the second switch are turned off in sequence.

[0085] The temperature of the PTC thermistor is monitored in real time and compared with a preset temperature threshold. If the temperature of the PTC thermistor is higher than the preset temperature threshold, the remaining energy in the energy feedback unit is used to start active cooling of the PTC thermistor until it reaches below the standard value.

[0086] The thresholds, such as the first threshold, the second threshold, and the third threshold, depend on the specific system parameters and can be determined by those skilled in the art through experiments or system simulations, and will not be elaborated here.

[0087] The workflow of the method of the present invention can be described as follows:

[0088] When the system is running normally, the first and second switches are open, the PTC current-sensitive resistor is in a low-resistance state, and the device has no effect on the system. At this time, the PT neutral point is directly grounded (preferably, in order to improve the stability of the system, the PT neutral point is directly grounded through a low-resistance fixed resistor, and the neutral point reconstruction unit and the energy reconstruction unit are connected in parallel with the fixed resistor).

[0089] When the system is disturbed, the PT excitation current increases slightly, and the PTC resistance begins to increase slightly. When the rate of change of the primary voltage of the PT exceeds the preset first threshold, the first switch is immediately closed, the adjustable inductor is engaged, and the system's inductive reactance to ground is changed instantaneously to suppress the occurrence of resonance.

[0090] Simultaneously or shortly after the first switch closes, the second switch closes, starting the bidirectional converter. This converter operates in "active damping" mode, absorbing residual electromagnetic energy in the system on one hand, and inverting this energy into a power frequency feedback system on the other (preferably, in actual connection, the energy feedback to the system needs to be connected to the bus or load via the AC side of a DC / AC converter), achieving a green energy cycle.

[0091] After the voltage stabilizes and the high-frequency harmonics disappear, the first switch is disconnected to exit the neutral point reconfiguration unit. Then, the energy feed unit is controlled to release the remaining energy, and finally the second switch is disconnected. At the same time, if the PTC current-sensitive resistor is too hot, the fan is activated for forced air cooling to quickly restore it to normal.

[0092] The system parameters, resonant frequency, optimal suppression strategy (inductance value) recorded each time resonance is successfully suppressed are associated with the system operating conditions (such as load size and switching operation type) to form a continuously growing database.

[0093] When a similar situation occurs again, the central controller can use case reasoning to directly retrieve the historical best strategy from the database for pre-configuration, greatly shortening the suppression response time and achieving the effect of intelligent learning of the system.

[0094] like Figure 2 As shown, this embodiment of the invention also provides a PT ferromagnetic resonance adaptive cooperative suppression system, comprising the following modules:

[0095] The collaborative suppression module is used to monitor signals in the circuit system, provide early warning of resonance, and instantaneously change the neutral point impedance parameter of the system after the resonance begins to disrupt the resonance condition, and absorb and feed back the resonance energy in the system.

[0096] The central control module is used to receive signals monitored by the cooperative suppression module and control the operation of the cooperative suppression module.

[0097] In some embodiments, the cooperative suppression module includes a high-voltage end sensing unit, a neutral point reconstruction unit, and an energy feedback unit; wherein...

[0098] The high-voltage sensing unit is connected between the high-voltage terminal of the PT primary side and the system bus, and is used to collect the voltage and current signals of the PT primary side in real time, including a PTC thermistor and a current transformer connected in series.

[0099] The neutral point reconfiguration unit is connected between the PT neutral point and ground, and is composed of a first switch and an adjustable inductor connected in series.

[0100] The energy feedback unit is connected in parallel with the neutral point reconfiguration unit and is composed of a second switch, a bidirectional DC / AC converter, and a DC-side support capacitor connected in series.

[0101] In some embodiments, a cooling module, driven by the DC output of the energy feedback unit, is also included for rapidly dissipating heat from the PTC thermistor after the resonance threat is detected to be eliminated; the cooling module may be a fan.

[0102] The PT ferromagnetic resonance adaptive cooperative suppression system according to embodiments of the present invention can correspond to performing the method described in the embodiments of the present invention, and the other operations and / or functions of each module / unit of the PT ferromagnetic resonance adaptive cooperative suppression system are respectively for implementing Figure 1 For the sake of brevity, the corresponding processes of each method in the illustrated embodiments will not be described in detail here.

[0103] The following example is a 10kV neutral-point ungrounded distribution network system. This system has a Y0-connected electromagnetic voltage transformer (PT) on its busbar, whose excitation characteristics enter the saturation region above 1.9 times the rated voltage. The system's phase-to-ground capacitance is approximately 0.1μF.

[0104] The selection of each component in the system is as follows:

[0105] High-voltage sensing unit

[0106] Connection method: Connected in series between the high voltage terminal (phase A) of the primary side of the PT and the system bus; In actual systems, this unit can be installed on the primary side of all three phase PTs, or only on the phase most prone to resonance;

[0107] PTC thermistor: High-voltage PTC is selected, with a normal resistance (25℃) of 12Ω. Under the action of fault current, the resistance can quickly jump to the kiloohm level, which can play the role of current limiting and generating monitoring voltage signal.

[0108] Current transformer: A 100:1 precision miniature current transformer is selected to collect the primary side current signal, and its output is sent to the central control module.

[0109] Voltage sampling: The voltage across the PTC is sampled using a high-resistance resistor divider (e.g., two 1GΩ resistors in series) to accommodate high-voltage environments.

[0110] Neutral point reconstruction unit

[0111] Connection method: Connected between the neutral point of the PT and the ground;

[0112] Key points clarified: To ensure normal system operation, the PT neutral point is permanently grounded directly through a 0.5Ω low-resistance circuit to meet measurement and protection requirements. The neutral point reconfiguration unit is connected in parallel with this low-resistance circuit as an additional branch.

[0113] First switch: High-voltage vacuum contactor is selected, which has the ability to close quickly (action time <50ms).

[0114] Adjustable inductor: An adjustable inductor based on a magnetic valve type controllable reactor (MCR) is adopted, with an inductance adjustment range of 0.1H ~ 5H. The inductance is continuously changed by adjusting its DC control current.

[0115] Energy Feedback Unit

[0116] Connection method: It is connected in parallel with the neutral point reconstruction unit, that is, it is also connected between the PT neutral point and the ground;

[0117] Second switch: A thyristor switching switch is selected to achieve arc-free and rapid connection (microsecond level).

[0118] Bidirectional DC / AC converter: adopts full-bridge IGBT topology, rated power 5kW, DC side voltage support range is 500V-800V DC;

[0119] DC-side support capacitor (DC-side capacitor): Select a 4500μF / 900V electrolytic capacitor bank;

[0120] Feedback path: The AC output of the converter is connected to the low-voltage side (0.4kV) of the station service transformer on the 10kV bus through an isolation transformer (400V / 10kV ratio), thereby realizing energy feedback to the system.

[0121] Central control module

[0122] Core processor: TI TMS320F28335 DSP, responsible for signal processing, logic judgment and PWM wave generation;

[0123] Sampling and Signal Conditioning: A 16-bit precision, 1MHz sampling rate ADC chip is configured to synchronously sample voltage and current signals. The signal conditioning circuit includes an anti-aliasing filter and an amplifier.

[0124] Cooling module

[0125] It consists of a 12V DC cooling fan, and its power supply is provided by the DC side of the energy feedback unit through a Buck step-down converter (which reduces 500V to 12V).

[0126] Based on system simulation and field tests, the key parameters for this embodiment are set as follows:

[0127] First threshold (voltage change rate): >5kV / ms; when the voltage change rate across the PTC thermistor exceeds this value, it is determined to be the start of resonance.

[0128] Second threshold (harmonic content, taking the 3rd harmonic as an example): >15%; used to confirm the occurrence of ferromagnetic resonance;

[0129] Third threshold (harmonic content, recovery criterion): <3%. Used to determine that the resonance threat has been eliminated;

[0130] First time threshold (waiting time for energy feedback unit to be deployed): 100ms;

[0131] Second time threshold (duration of recovery criterion): 2s;

[0132] Temperature threshold (start-up cooling): 60℃.

[0133] Workflow details:

[0134] Phase 1: Normal Operation

[0135] The neutral point of the PT is reliably grounded through a fixed resistor of 0.5Ω;

[0136] Both the first switch and the second switch are in the off state;

[0137] The high-voltage sensing unit continuously monitors the system, and the PTC is in a low-resistance state (approximately 12Ω), so its impact on the system is negligible.

[0138] The central control module calculates the voltage change rate and harmonic content in real time, and the values ​​are all within the normal range.

[0139] Phase Two: Resonance Occurrence and Suppression

[0140] Disturbance and warning: The system is disturbed due to the disappearance of a single-phase ground fault; the PT core begins to saturate, the primary current changes drastically, and the voltage change rate across the PTC reaches 8kV / ms within 2ms, exceeding the first threshold (5kV / ms).

[0141] Rapid reconfiguration of the neutral point: The central control module immediately issues a command to close the first switch and activate the neutral point reconfiguration unit;

[0142] The central control module estimates the system's capacitance to ground and the PT's magnetizing inductance based on the current transformer current and the PT secondary voltage. FFT analysis displays the main resonant frequencies, and the inductance value of the adjustable inductor is adjusted accordingly.

[0143] Within 100ms after the first switch is activated, as long as the harmonic content is higher than the second threshold, the central control module will control the second switch to close and start the energy feedback unit.

[0144] The bidirectional converter operates in current control mode. By detecting the harmonic components in the neutral point current, it generates a PWM current with the opposite phase, absorbing the 125Hz resonant energy into the DC-side capacitor.

[0145] When the DC-side capacitor voltage rises to 750V, the converter switches to voltage control mode, converting DC energy into 50Hz power frequency current, which is then fed back to the 0.4kV system through an isolation transformer.

[0146] Under the combined effect of neutral point reconstruction and energy feedback, resonance was suppressed; the central control module detected that the harmonic content dropped below the third threshold, and this state lasted for 2 seconds.

[0147] First, disconnect the first switch and exit the neutral point reconstruction unit;

[0148] Then the converter is controlled to fully feed back the remaining energy in the DC side capacitor. After the DC side capacitor voltage drops to 500V, the second switch is disconnected.

[0149] The temperature sensor showed the PTC temperature to be 68℃ (above the temperature threshold); the central control module activated the Buck converter, driving the cooling fan to force-cool the PTC. After approximately 3 minutes, the PTC temperature dropped to 45℃, and the fan automatically stopped.

[0150] Compared with traditional fixed harmonic suppression devices, this embodiment demonstrates the following advantages:

[0151] Response speed: The entire response time from disturbance to the activation of the first switch is less than 5ms, achieving "ultra-early" suppression and avoiding the formation of overvoltage.

[0152] Adaptive capability: The adjustable inductor can automatically adjust to the optimal value according to the frequency characteristics of each resonance (division frequency / power frequency / high frequency), which significantly improves the success rate of suppression.

[0153] Energy utilization: In this embodiment, the energy feedback unit recovers approximately 0.8 kWh of electrical energy in a single operation and feeds it back to the station's power system, demonstrating energy-saving benefits.

[0154] System recovery: The orderly exit and active cooling mechanism ensures that the device can quickly return to standby status, improving the availability and lifespan of the equipment.

[0155] If the above functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0156] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-including system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0157] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0158] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0159] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

[0160] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for adaptive cooperative suppression of PT ferromagnetic resonance, characterized in that, include: The voltage signal, current signal, and PT secondary voltage signal monitored by the high-voltage end sensing unit are sampled in real time to calculate the primary voltage change rate and harmonic content; the high-voltage end sensing unit is connected between the PT primary high-voltage end and the system bus. Based on the calculation of the primary voltage change rate and harmonic content, and the comparison with the corresponding preset threshold, the neutral point reconstruction unit is controlled to be put into operation, and the resonance condition is destroyed by changing the neutral point grounding impedance. After the neutral point reconstruction unit is operational, the energy feedback unit is controlled to absorb resonant energy and feed it back to the power system. Once the resonance threat is detected and eliminated, the control sequentially shuts down the neutral point reconstruction unit and the energy feedback unit, and uses the remaining energy in the energy feedback unit to initiate active cooling of the high-voltage sensing unit.

2. The adaptive cooperative suppression method for PT ferromagnetic resonance according to claim 1, characterized in that, The high-voltage sensing unit is used to collect the primary voltage and current signals of the PT in real time, including a PTC thermistor and a current transformer connected in series. The neutral point reconfiguration unit is connected between the PT neutral point and ground, and is composed of a first switch and an adjustable inductor connected in series. The energy feedback unit is connected in parallel with the neutral point reconfiguration unit and is composed of a second switch, a bidirectional DC / AC converter, and a DC-side support capacitor connected in series.

3. The adaptive cooperative suppression method for PT ferromagnetic resonance according to claim 2, characterized in that, The neutral point reconstruction unit is controlled based on the calculated primary side voltage change rate and harmonic content. The resonance condition is disrupted by changing the neutral point grounding impedance. The specific process is as follows: The primary voltage change rate is set as the main criterion. When the primary voltage change rate exceeds the preset first threshold, the first switch is immediately triggered to close, and the neutral point reconstruction unit is put into operation. After the complete harmonic analysis is finished and the harmonic content is obtained, the harmonic content is compared with the preset second threshold: If the harmonic content is less than or equal to the preset second threshold, it is determined that no resonance characteristic has occurred, and the first switch is turned off, and the neutral point reconstruction unit is launched. If the harmonic content is greater than the preset second threshold, it is confirmed that ferromagnetic resonance has occurred, and the neutral point reconstruction unit is maintained.

4. The adaptive cooperative suppression method for PT ferromagnetic resonance according to claim 3, characterized in that, The process for determining the value of the adjustable inductor is as follows: While the neutral point reconfiguration unit is being put into operation, the system ground capacitance and PT excitation inductance are estimated based on the current signal monitored by the current transformer and the secondary voltage signal of the PT, and the main frequency of the current resonance is determined. The type of resonant frequency is determined based on the main frequency, the target value is calculated using the corresponding formula, and the adjustable inductor is adjusted to the target value. Continue monitoring. If the resonance is not suppressed, adjust the adjustable inductor in a preset step size near the target value until the resonance is suppressed, and record the corresponding frequency and inductance value. If resonance is suppressed, keep the adjustable inductance at the target value and record the corresponding frequency and inductance value.

5. The adaptive cooperative suppression method for PT ferromagnetic resonance according to claim 2, characterized in that, After the neutral point reconfiguration unit is operational, the energy feedback unit is activated to absorb resonant energy and feed it back to the power system. The specific process is as follows: After the neutral point reconstruction unit operates, if the harmonic content is detected to be greater than the preset second threshold within the preset time threshold, the second switch is closed and the energy feedback unit is started. If the harmonic content is not detected within the preset first time threshold, the second switch will be closed directly when the preset first time threshold is reached, and the energy feedback unit will be started. By using PWM modulation of a bidirectional DC / AC converter, resonant energy is absorbed into the DC-side support capacitor and inverted into power frequency energy to be fed back to the system or load, thus achieving smooth energy absorption and feedback.

6. The adaptive cooperative suppression method for PT ferromagnetic resonance according to claim 2, characterized in that, Once the resonance threat is detected and eliminated, the control sequentially shuts down the neutral point reconstruction unit and the energy feedback unit, and uses the remaining energy in the energy feedback unit to initiate active cooling of the high-voltage sensing unit. The specific process is as follows: When the detected harmonic content is lower than the preset third threshold and the duration reaches the preset second time threshold, the first switch and the second switch are turned off in sequence. The system compares the temperature of the PTC thermistor, which is detected in real time, with a preset temperature threshold. If the temperature of the PTC thermistor is higher than the preset temperature threshold, the remaining energy in the energy feedback unit is used to start active cooling of the PTC thermistor until it reaches below the standard value.

7. A PT ferromagnetic resonance adaptive cooperative suppression system, applied to the PT ferromagnetic resonance adaptive cooperative suppression method according to any one of claims 1-6, characterized in that, include: The collaborative suppression module is used to monitor signals in the circuit system, provide early warning of resonance, and instantaneously change the neutral point impedance parameter of the system after the resonance begins to disrupt the resonance condition, and absorb and feed back the resonance energy in the system. The central control module is used to receive signals monitored by the cooperative suppression module and control the operation of the cooperative suppression module.

8. The PT ferromagnetic resonance adaptive cooperative suppression system according to claim 7, characterized in that, The collaborative suppression module includes a high-voltage end sensing unit, a neutral point reconstruction unit, and an energy feedback unit; wherein... The high-voltage sensing unit is connected between the high-voltage terminal of the PT primary side and the system bus, and is used to collect the voltage and current signals of the PT primary side in real time, including a PTC thermistor and a current transformer connected in series. The neutral point reconfiguration unit is connected between the PT neutral point and ground, and is composed of a first switch and an adjustable inductor connected in series. The energy feedback unit is connected in parallel with the neutral point reconfiguration unit and is composed of a second switch, a bidirectional DC / AC converter, and a DC-side support capacitor connected in series.

9. The PT ferromagnetic resonance adaptive cooperative suppression system according to claim 8, characterized in that, It also includes a cooling module, driven by the DC output of the energy feedback unit, for rapidly dissipating heat from the PTC thermistor after the detected resonance threat has been eliminated.

10. A computing device for an adaptive cooperative suppression method of PT ferromagnetic resonance, characterized in that, include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs including instructions for performing the method according to any one of claims 1-6.

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